Comment by pjmlp

On the contrary, GNU Compiler Collection is written in C++ and happens to have C as one of the supported fronteds, having moved away from C in 2008.

LLVM is written in C++, also supports multiple language frontends, one of them happens to be C.

Visual C++, also written in C++, happens to still compile some form of C, and after adding some C11 and C17 support (a few items are still missing in 2026), Microsoft is in no rush to add anything else.

The language that matters is the implementation, otherwise we can also talk about the relevance of PL/I compilers from IBM and Unisys, written in C++.